[mirimir]

Here's a famous counterexample: http://www.anapsid.org/cnd/hormones/sabotage3.html

tl;dr: Sonnenschein and Soto were studying effects of estrogens on in vitro proliferation of breast cancer cells. Their assays stopped working. Eventually they figured out that Corning had added p-nonylphenol, which is estrogenic, to the plastic, to reduce brittleness.